Phylogenetic Interrelationships among Baculoviruses: Evolutionary Rates and Host Associations

The phylogenetic relationship of several baculovirus polyhedrin genes was investigated. Alignments of 18 polyhedrin gene amino acid sequences from which 12 were also available as DNA sequences were constructed based on positional homology and trees were calculated using character state and distance methods. Our results indicate that the Hymenopteran NsSNPV diverged from the Lepidopteran baculovirus before the separation of the NPV from the GV and subsequent radiation of these Lepidopteran groups. Moreover, this analysis indicates that lepidopteran NPV are clustered in at least two groups with distinct evolutionary rates. Group I includes the AcMNPV, BmMNPV, BmSNPV, OpMNPV, AgMNPV, and possibly the GmMNPV and AsMNPV. Group II includes the MbMNPV, PfMNPV, SfMNPV, SeMNPV, and possibly the OpSNPV. This grouping is also supported by a tree constructed from sequence data from the 5′ untranslated leader region of the polyhedrin gene. Furthermore, the polyhedrin-based phylogeny was analyzed for its congruence to the genomic organization and other biological characteristics of the baculoviruses. This study shows that the SNPV and MNPV morphotypes have to be taken with caution as classificatory traits since they appear to be unpolarized. In addition, the comparison of the baculovirus phylogeny with the Lepidoptera phylogeny confirms the assumption that the evolutionary history of the baculoviruses is not entirely in agreement with the taxonomic organization of the Lepidoptera, implying that the common designation of baculoviruses based on the hosts may not be adequate for baculovirus classification since it does not reflect the genetic relatedness of the viruses. We suggest that baculovirus taxonomy should take in consideration a concept of species based on relevant viral characteristics other than the first documented host and viral morphotype.